New bird flu jumped directly from chickens

LONDON -- Chinese scientists have for the first time found strong evidence of how humans became infected with a new strain of bird flu: from chickens at a live market.

The scientists compared swabs from birds at markets in eastern China with virus samples from four patients who caught the new H7N9 virus. They found the virus from one patient was nearly identical to one found in a chicken. The research was published online yesterday in the journal Lancet.

Proving definitively how patients were infected is difficult and experts have struggled to find much virus in birds. Despite taking nearly 48,000 samples from animals in live markets, Chinese officials found only 39 positive tests for H7N9. Birds in live markets were the suspected source of infection but experts weren't sure whether other animals or wild birds might also be responsible.

Health officials have so far refrained from recommending any wide-scale slaughter of poultry to contain the disease, one of the main tools used to combat the bird flu strain, H5N1. Unlike that strain, H7N9 doesn't appear to sicken chickens, giving experts fewer signs as to where it might be spreading.